We don't call __add_pages() directly in the function add_memory()because some other architecture related thins needs to be donebefore or after calling __add_pages(). So we should not call__remove_pages() directly in the function remove_memory.Introduce new function arch_remove_memory() to revert the things donein arch_add_memory().

Note: the function for x86_64 will be implemented later. And I don'tknow how to implement it for s390.